How do you have a "50V 4A" signal if it's going through minimum 0.91kohms (= 55mA worst case)?
Bandwidth is unstated, so it's anyone's guess if this is DC (a mechanical or MOS relay would do) or RF (mechanical relay, or a much more complicated active circuit).
Switching speed is also unstated.
Polarity is also unstated, though if your diagram is to be taken at face value, it seems the op-amp only outputs negative voltages? (In other words, your circuit won't "switch" while the op-amp output is positive: that's what the little triangles in the MOSFET symbol are there for, they indicate the internal body diode.)
If it is bipolar (positive and negative voltage wrt ground), you need a bidirectional switch. Usually, a pair of MOSFETs are connected together source-to-source, with the switch terminals being the two drains. An isolated gate driver is needed to turn it on and off. PhotoMOS SSRs do this, with a handy optocoupler, all in one package. But they're quite slow (~milliseconds), so they're not suitable for everything.
If you only need two resistor settings (not open circuit), consider using one "default" resistor, and switching another in parallel with it. To get 1 or 10k, you'd use 10k and 1.11k resistors, with only one switch for the 1.11k resistor.
You may be better off harnessing features of the power op-amp. If it has a "mute" or "disable" or "power down" option, that should leave the output open-circuit, which is the same as opening a switch. Use one amp to drive each resistor you need. This has the advantage that it's fast (as fast as the internal circuitry), and is limited only by op-amp performance (so a similar method can be used all the way up into RF, if needed).
Tim